It is well known that humans have the ability to recognize the source of a sound using their ears even without any visual cues. Humans estimate the location of a source by taking cues derived from one ear, and by comparing cues received at both ears (difference cues or binaural cues). Among the difference cues are time differences of arrival and intensity differences. The monaural cues come from the interaction between the sound source and the human anatomy, in which the original source sound is modified before it enters the ear canal for processing by the auditory system.
In a real-world situation the sound actually emanates from a particular location. It can be desirable to enable the listener to perceive that sound produced by audio-speakers appears to come from a particular location in 3-dimensional space. One possible technique involves having the user wear “head-phones,” also referred to as a “headset.” That is, one audio-speaker is placed over or near each ear. This technique may employ creating an audio signal using a “head-related transfer function” (HRTF) to create the illusion that sound is originating from a location in 3D space. Herein, an audio signal that creates the illusion that sound is coming from a location in 3D space is referred to as a 3D audio signal.
An HRTF may be defined based on the difference between a sound in free air and the sound as it arrives at the eardrum. The HRTF describes how a given sound wave input (parameterized as frequency and source location) is filtered by the diffraction and reflection properties of the head and pinna, before the sound reaches the eardrum and inner ear. An HRTF may be closely related to the shape of a person's head and physical characteristics of their ears. Therefore, the HRTF can vary significantly from one human to the next. Thus, while HRTF's may be used to help create a 3D audio signal, challenges remain in tailoring the HRTF to each user.
One possible use of 3D audio is in augmented reality scenarios. Augmented reality may be defined as using some computer generated technique to augment a real world situation. Augmented reality, as well as other 3D applications, requires accurate 3-D audio. For example, a user should be able to accurately localize a sound as coming from a virtual sound source.
While techniques for 3D audio may exist, improvements are desired. As already noted, one improvement is to provide an accurate HRTF for the user. However, other improvements are also desired. A 3D audio signal should be accurate, consumer friendly, cost effective, and compatible with existing audio systems.